Grafting Tomatoes

Grafted tomatoes bring together the best of both worlds: excellent production and disease resistance, even on the fussiest varieties.

“We’ve seen a yield boost of 30 to 50 percent,” says Andrew Mefferd, tomato expert at Johnny’s Selected Seeds. “[The plants] go on forever. They have so much stamina. They keep fruiting until frost.”

Grafting is simply taking the top (scion) of any tomato variety seedling that is the same stem size as the rootstock, and attaching it to a specialized hybrid rootstock grown specifically for its vigor and disease resistance. The rootstock provides protection from tomato mosaic virus, nematodes, verticillium wilt, and a number of diseases based upon that specific rootstock. For instance, ‘Brandywine’ tomatoes succumb to a number of diseases. If they’re grafted to ‘Estamino’ rootstock, which is resistant to seven tomato disease issues, they garner that benefit.

Jack Manix, of Walker Farm in Dummerston, Vermont, needed some way, short of removing the soil completely, to combat soilborne pathogens in his greenhouse tomato-growing operation.

“We grow organically, but can’t follow one of the main principles: crop rotation,” he says. “We had to try something different.”

They began grafting all of their ‘Buffalo’ variety (which Manix says is an excellent-tasting tomato on a wimpy plant), and never lost one. Now they graft all of their own, as well as 3,500 plants for other growers.

Grafting is a huge boon for commercial growers and small farms producing for the market, but it’s also a benefit for home growers who want to grow heirlooms or varieties that otherwise produce marginally in their region.

There are plenty of grafted plants available, but gardeners looking for an organic alternative will probably have to create it themselves.

Tomato grafting isn’t difficult, but it requires a little practice and an investment in the rootstock seed, which can cost nearly 50 cents per seed. Grafting clips, either the small silicon clips for top grafting (roughly $.14 apiece) or the spring-loaded larger grafting clips ($.44 per clip), are the best to use since they are easy to attach and are reusable. Some people try using tape or even grafting tape, but it’s a challenge with the delicate tomato stems.

“It’s something for the really serious home gardener,” says Mefferd.

The most important part of a grafted plant is the rootstock. There is a growing number of options out there, although most are not organic seed.

Johnny’s offers organic seeds of the variety ‘Estamino’. It’s a “generative” type rootstock, which means it puts more energy into fruit production rather than plant growth. The drawback is it doesn’t handle stress as well as the “vegetative” types, such as ‘Maxifort’, a standard for many growers because of its exceptional growth and durability.

Mefferd says with the generative rootstock, “You may have better luck with smaller fruit and shorter crop time.” It’s ideal in areas such as the Pacific Northwest where heat stress is not an issue.

On the other hand, the vegetative rootstock is good for big-fruited tomatoes, long seasons, plus it handles the heat well.

For the scion, you can use practically any top variety you want, although if it’s well matched, such as small-fruit tomatoes on a generative rootstock or the larger varieties on the vegetative kind, you’ll have better success.

As a general rule, start your rootstock and scion plant at the same time so the stem diameters match when it’s time to graft.

Types of Grafts

One of the simplest grafts is a top graft. Mefferd recommends working with small plants, which might be only 2 to 3 inches tall, not only to fit the silicone grafting clip size but to increase success.

Choose a rootstock plant and scion that are nearly identical in stem diameter. Carefully cut the rootstock plant at approximately a 35-degree angle with a razor, and discard the top. Using the same angle, slice off the top of the scion. Some people pinch off several of the scion’s leaves to reduce respiration.

Pinch the clip and slide it over the rootstock stem with half of the clip above the stem in order to receive the scion. Slide the scion into the grafting clip, matching the angles as perfectly as possible.

Support the plant with a bamboo skewer or toothpick, and place a plastic bag over the container to create a humid environment. Keep the newly grafted plant in a darkened, warm area to reduce growing stress on the plant. At this time, it needs to put energy towards healing. A warm, shaded area is fine, or at the very least out of the direct sunlight. Keep it here for at least 4 to 5 days; even up to a week. If it wilts immediately, it didn’t take.

Take your time returning it to direct sunlight or grow lights. Depending on the intensity, it might require another week under more subtle lighting. There’s no need to take off the clip; it will fall off on its own.

Manix uses the side graft, also known as the approachgraft, in which larger plants are sliced partway through the stem at a 45-degree angle. One angle is slid into the other, and the plants are attached with a spring-loaded grafting clip. Cut off the top of the rootstock and the roots of the scion after 4 to 5 days. You can take off the grafting clip in a few more days.

When you’re planting your grafted plant, don’t bury the graft below the soil, because the scion can root and negate the reasons you grafted in the first place.

And don’t be afraid to prune. Both Manix and Mefferd say grafted plants thrive under the knife.

“If you want to stick a plant in the tomato cage and watch it grow, don’t get a graft,” says Mefferd. You need to actively prune it throughout the season, because the plants grow incredibly quickly. By pruning, you’re allowing it to send more of that energy to fruit production.

Grafted plants are great way to grow your favorite tomato in huge amounts. Once you start grafting, you might never settle for less.